Insurance Activity - Additional Information (Detail) (USD $)	6 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2013	Dec. 31, 2012	Mar. 19, 2012	Aug. 31, 2009
Quoted percentage to share base					50.00%
Balances in the fair market reserve		$ 51,200,000	$ 52,200,000
Loss contract fair market reserve		51,230,000	52,217,000	63,100,000
Decreased value of fair market reserve			10,900,000
Decrease in expense	$ 10,700,000	$ 1,000,000
WMMRC [Member]
Second loss layer risk percentage of range minimum					5.00%
Second loss layer risk percentage of range maximum					10.00%
First loss layer risk percentage of range minimum					4.00%
First loss layer risk percentage of range maximum					5.00%
Minimum period of reinsurance agreements		5 years
Maximum period of reinsurance agreements		10 years